What was the timetable for British development for their 20 mm cannon
ammuniation during WW2?

They also used ball ammo early on (just an empty steel shell - we'd
call it Target Practice now) in lieu of AP - it would punch through
about a half-inch of plate, and sometimes proved more destructive
initially than the fast-fuze HE. They continued to use ball mixed with
HE/HEI in the belts until 1942, when the SAPI came along. This was
just an HE shell filled with incendiary material and with a hard steel
piercing cap instead of a fuze; it could penetrate around 20mm plate.
From then on, the standard belt mix was two HEI followed by two SAPI.

Thanks Tony!

So RAF stopped using ball ammo during 1942.
And there was no true AP ammo in use before SAPI?

Interesting. I wonder, they had Hurricane II with 4x20 mm. I presume
this plane was used in ground attack missions with the bombload. Those
cannons were still loaded with HE/HEI/BALL ammo for strafing missions? I
presume they weren't much effective against German armour?

I have Tony/Emmanuel's book and it mentions how RAF tested the cannon
ammo against Japanese tanks. Knowing how Japanese tanks had rather thin
armour I'd guess the results were better against them than against
German armour, excepting Panzer IIs and other light tanks/vehicles?

So RAF *never* had a true AP shot? During whole war? Fascinating.

This development on cannon ammo is a fascinating subject. I was quite
astounded when I interviewed the Finnish ace Antti Tani, who was one of
the best Finnish Morane-Saulnier 406 pilots. They had only HE ammo
available and it is quite wide opinion in Finland, that the Morane
cannon was very problematic. The ammo was so sensitive, that it
sometimes exploded in the cannon barrel - or in the surface of the
target, just like Brits found out. One squadron made tests and mr. Hugo
Estama referred, that the cannon shot exploded even when hitting a
cardboard, before penetrating.

Mr. Tani on the other hand was a quick learner and he actually made AP
ammo by himself. He defused the HE rounds, took out the HE and voila -
self made AP. Similar to British ball? He loaded his cannon himself, 2
HE for 1 "AP". This practise was discontinued by commander's order when
somebody else in the squadron tried making "AP" rounds too and the shot
exploded, wounding him severely. Mr. Tani was a mechanic, watchmaker by
profession, so he knew what he was doing. He claimed total of 7 Soviet
planes with Morane, including two of the most valuable prey out there -
Pe-2 bombers (which almost had higher cruising speed than the Morane's
top level speed).

If your'e interested you can read mr. Tani's interview he
http://www.virtualpilots.fi/hist/WW2...riEnglish.html

jok